gpssh errors out with "unable to login to <hostname>" and "Could not acquire connection"

Products

• VMware Tanzu Greenplum

Issue/Introduction

Attempting to use gpssh results in the following error:

gpssh -h <hostname>
[ERROR] unable to login to <hostname>
Could not acquire connection.

Environment

Product Version: 6.25

Resolution

This is a symptom of not setting MaxStartups and MaxSessions high enough in sshd_config. Documentation is at https://docs.vmware.com/en/VMware-Greenplum/6/greenplum-database/install_guide-prep_os.html#ssh-connection-threshold. Raising these properties should stop the error from occurring.